Some mobile communication devices such as a mobile phone and a PHS (Personal Handy-phone System) include various functions in addition to a communication function. For example, Patent Literature 1 discloses a portable image transmitter. The portable image transmitter includes a main body that integrates an image input unit such as a camera, a transmission unit, a display unit, and an operating unit. The transmission unit digitalizes and compresses an output video signal from the image input unit so as to generate an output signal to a public line. The transmission unit also receives a signal from the public line, and then demodulates and decodes the signal. The display unit displays the decoded the video signal. The operating unit operates the respective devices. The portable image transmitter further uses a detachable mobile phone so as to establish connection with the public line.